The official team website listed players expected to start at each position. Kupp and Webster were both considered surprises on the depth chart (via TheRams.com):

Kupp likely made the list of starters because the list is based on a three wide receiver set. He would be alongside Tavon Austin and Robert Woods, according to the projection. Webster was mainly a special teams contributor in his first four seasons with the Broncos, and signed with the Rams because of the opportunity to earn a starting role. It doesn’t hurt that the cornerback played under defensive coordinator Wade Phillips for the last two years in Denver.

Before he was signed to Los Angeles, teammates on the Broncos said they expected Webster could start for an NFL team.

I know the #Rams have serious interest in Kayvon Webster.That could be good landing spot. His teammates believe he could be a starter in NFL